Several, naturally-occuring, polyether antibiotics (e.g. monensin) have been reported to increase feed utilization in ruminants; U.S. Pat. No. 3,839,557. A variety of macrocyclic polyether compounds having a carboxy group directed into the polyether ring have been described in U.S. Pat. No. 3,965,116 and Journal of the American Chemcial Society, 97, 1257 (1975), but none of these compounds was reported to have feed utilization efficiency increasing properties.